This invention relates to a signal processing apparatus and a signal processing method, a program, and a recording medium, and more particularly to a signal processing apparatus and a signal processing method, a program, and a recording medium by which a feature value of an audio signal such as the tempo is detected with a high degree of accuracy.
Various methods are known by which the tempo of an audio signal of, for example, a tune is detected. According to one of the methods, a peak portion and a level of an autocorrelation function of sound production starting time of an audio signal are observed to analyze the periodicity of the sound production time, and the tempo which is the number of quarter notes for one minute is detected from a result of the analysis. The method described is disclosed, for example, in Japanese Patent Laid-Open No. 2002-116754.
However, according to such a method of detecting the tempo from the periodicity of sound production time of a peak portion of an autocorrelation function as described above, if a peak appears at a portion corresponding to an eighth note in an autocorrelation function, then not the number of quarter notes for one minute but the number of eighth notes is likely to be detected as the tempo. For example, also music of the tempo 60 (the number of quarter notes for one minute is 60) is sometimes detected as music of the tempo 120 wherein the number of peaks for one minute, that is, the number of eighth notes, is 120. Accordingly, it is difficult to accurately detect the tempo.
Also a large number of algorithms are available for detecting the tempo instantaneously from an audio signal for a certain short period of time. However, it is difficult to detect the tempo of an overall tune using the algorithms.